Get Parcel Gap

Parcel codes we know about that Roost cannot show, both ways round.

Frederick, 2026-09-18 (#1750): "there should never be a parcel code that's not in our system", and "we have to be able to search and find if there's any items that haven't been printed that should have been printed."

parcel_code narrows the first list to one code, which is how somebody holding a label asks about the thing in their hand.

2026-10-09 (Frederick: "yes"): a code with no parcel row that the mail service printed is left out of no_parcel_row and with_no_parcel_row, and counted in summary.printed_by_the_mail_service_without_a_record. A search for that code still finds it, with the reason printed_by_the_mail_service. See parcel_gap's module docstring.

⛔READ summary.never_asked_about AND summary.could_not_be_asked_about BEFORE READING AN EMPTY never_printed AS GOOD NEWS. Both are pieces we have no answer for, and on staging -- which holds production's physical-mail pair and 403s on every vendor read -- the second is every piece there is. See parcel_gap's own module docstring.

Had only test callers from 2026-09-18 until issue #2323 (R-212): a real screen (apps/web/src/pages/fulfillment/ParcelGapCard.tsx, on Fulfillment

Print batches) now calls this route.